Stretch films are widely used in a variety of bundling and packaging applications. For example, stretch films have become a common method of securing bulky loads such as boxes, merchandise, produce, equipment, parts, and other similar items on pallets. Stretch films are typically made from various polyethylene resins and may be single or multilayer products. An additive known as a cling agent is frequently used to ensure that adjacent layers of film will cling to each other.
An issue with conventional stretch films is that the edges of the film can be easily damaged, which may result in tearing or failure of the film during use. Typically, the edges of the film are prepared by transversely slitting individual roll widths of film from a wider width of film by means of a conventional sharp edge slitter assembly. Any defects that are introduced into the edges of the film during the slitting process can result in film failure during the application process. Dropping the film roll or any other abuse during handling may also create zones of weakness or tears in the edges of the film.
One method of reinforcing the edges of the film is to fold the edges of the film to form a hem. For example, U.S. Pat. No. 5,565,222 discloses an apparatus for hemming the edges of stretch film. The apparatus consists of a first hemming roller with a width less than the width of the film, guide bars located adjacent to the film's path of travel, and a second hemming roller. As another example, U.S. Pat. No. 5,531,393 discloses a film with folded edges. Folding is achieved by means of folding fingers that project inwardly from the side plates of the apparatus. In both of the previously mentioned methods, the folding is performed post-production in a separate and secondary process.
These hems, however, cause difficulties in winding a uniform roll of film due to the essentially double thickness of the hemmed edge as compared to the remainder of the film. Oscillating the film as it is wound onto the roll can prevent the hemmed edges from stacking on top of one another, thus producing a roll with uniform dimensions.
U.S. Pat. No. 5,531,393 discloses an apparatus where the roll onto which the film is wound is oscillated to prevent stacking of the folds in the film's edges. The oscillation is controlled by a piston reciprocating between two limit positions, which moves a cap inserted into the hollow end of the film roll. U.S. Pat. No. 5,967,437 discloses a means for oscillating the film, preferably by rectilinear motion of either the feed roller or the film roll along its axis. However, the disclosure results in film rolls with frustoconical or substantially conical end zones.
As can be seen, there is a need for methods, systems, and devices to produce uniform, flat rolls of film in-process so that they can be easily stored, transported, and used. There is also a need for methods, systems, and devices to make film rolls less susceptible to damage during shipment and use, thus reducing wastage. In addition, there is a need to facilitate the unwinding of the film, making the film easier for the operator to use.